Gas plating cerium



1962 F. E. DRUMMOND GAS PLATING CERIUM Filed Jan. 22, 1959 [RARE EARTH MEI'AL INVENTOR FoLsoM E. DRUMMOND SUBSTRATE (METAL, PAPER, GLASS, ETC) BY f/wnin Wnin/ ATTORNEYS United States Patent 3,049,797 GAS PLATING CERIUM Folsom E. Drummond, Washington, DC, assignor to Union Carbide Corporation, New York, N.Y. Filed Jan. 22, 1959, Ser. No. 788,326 2 Claims. (Cl. 29-194) This invention relates to gas plating of cerium, the invention being particularly adapted for depositing such metal using heat-decomposable metal compounds of cerium.

It has been proposed heretofore to gas plate the heavy metals, e.g., nickel, chromium, copper, etc., onto substrate surfaces, and employing thermally decomposable compounds of these heavy metals, for example, the carbonyls of these metals.

The deposition of cerium, however, has presented a diflicult problem because it is more reactive chemically than the heavy metals. Cerium reacts readily with oxygen, forming the metal oxides. This action takes place under ordinary atmospheric temperature and pressure conditions. It reacts also readily with silica to form silicates.

It is a principal object of this invention to provide a process for gas plating this rare earth metal onto substrates while protecting the same against oxidation or reaction with other substances.

In the process of the invention, a cerium metal bearing compound, or mixture of such compounds, is vaporized and admixed with an inert gas carrier such as dry helium or argon, and brought in direct contact with the substrate material to be metal plated, the substrate being heated to a temperature high enough to cause thermal decomposition of the rare earth metal bearing compound brought in contact therewith, whereby the metal constituent is deposited onto the surface of the substrate.

The optimum temperature employed in gas plating the rare earth metal varies, depending upon the rare earth metal compound and the conditions imposed. In general, the temperatures range from 5001000 C. Preferably an excess of inert carrier gas is used with respect to the gaseous rare earth metal compound.

Rare earth metals useful in practicing the invention are set forth in the following Table, together with their valencies and atomic weights:

The rare earths are very much alike chemically and, as noted from their atomic weight, vary over a range of 138 through 179.

Compounds of the rare earth metals such as acetylacetonates, hydrides, nitrides, etc., and organo-metal complexes are useful in carrying out the gas plating process. Either the liquid or gaseous form may be used, the same being introduced into a gas plating chamber and in contact with the heated substrate. During the gas plating operation, the substrate is maintained under an inert atmosphere. Subatmospheric or vacuum pressures are preferably employed to improve the the efficiency of the process and produce an adherent metal deposit.

An atmosphere of argon or helium, free of carbon dioxide, oxygen and water vapor, is employed to avoid oxidation reactions. The gas plating, Where desired, may be carried out at ordinary atmospheric pressure or above, provided the substrate surface to be plated is freed of occluded air, moisture or oxygen-carrying gases and the plating chamber is maintained filled with dry inert gas or admixture of inert gas with the heat-decomposable rare earth metal compound, the metal of which is to be deposited.

The invention will be more readily understood by reference to the following detailed description and accompanying drawings, wherein:

FIGURE 1 is a schematic illustration of a suitable apparatus for carrying out the gas plating process and showing a vertical cross-sectional view of the same as used to gas plate articles;

FIGURE 2 is a similar schematic illustration of a modified apparatus for gas plating long continuous-length strips, strands or filaments;

FIGURE 3 is a view in perspective showing a fragmentary portion of a gas plated sheet or strip of material, the same being illustrated as broken away and partly in section to show the integral outer layer of rare earth metal; and

FIGURE 4 is an enlarged fragmentary view in section of a substrate material gas plated With rare earth metal.

Referring more particularly to the drawings, FIGURE 1 illustrates an apparatus for gas plating articles, and comprising a gas plating chamber 10 which is heated by the external coil heating element 11. The coil may be heated electrically or by flowing heated fluid such as steam or the like through the coil.

A pump 12 draws a mixture of the gaseous metal. earth compound and carrier gas from a source and moves the same through a connector pipe 14 to the gas plating chamber 10. The pump 10 maintains a steady flow of plating gas to the plating chamber.

Mounted in the gas plating chamber 10 are racks 15 upon which objects or shapes to be gas plated may be supported. 'l hese racks 15 are spacedly arranged lengthwise of the chamber 10 on an insulated base member 16. The racks 15 preferably comprise ceramic discs 17. Chamber 10 is provided at the outer end with an outlet in which a tubing 18 is secured, the tubing 18 being bent downwardly and arranged to discharge into a condenser fluid or recovery tank 20 containing cooling water 21. A U-shaped trap 22 is surrounded by the cooling water 21 contained in the tank Zil. Water is circulated through the tank 20 through an inlet pipe connection 23 and outlet pipe overflow 24. The U-shaped trap 22 is provided with a discharge tube 26 for the emission of exhaust gases. A thermometer 27 is arranged to indicate the temperature in the gas plating chamber. In the modified apparatus illustrated in FIGURE 2, an elongated gas plating chamber 30 is depicted for gas plating long continuous strips or filaments. The plating chamber is heated by the coils 31, as in FIGURE 1, and is provided with an inlet pipe connector 32, and an outlet pipe 33 for introducing a gaseous heat-decomposable rare earth metal compound and inert gas carrier, e.g., helium or argon, into the gas plating chamber. The material 35 to be gas plated, e.g., metal, paper, glass, or the like, in the form of a sheet, strip or filament, is suitably drawn from a storage roll 36 and passed through a pie-heater chamber 37 and then through the gas plating chamber where it is plated; and then the plated material 38 is rolled up on a storage roll 39.

spears? The preheating chamber 37 is suitably mounted directly connected to the inlet opening 40 of the gas plating chamber 30, and electrical heating elements 41 and 42 are disposed above and below the strip 35 and centrally of the chamber 37 to provide even heating of the strip. The inlet and outlet openings 40 and 41 are suitably sealed against leakage of gases into the gas plating chamber so that oxidation of the gases or material is prevented. Where desired, the plated material may be cooled to room temperature before exposure to air.

In carrying out the process of the invention to coat the substrate material with the resistive coating of the rare earth metal, the preheater 37 or temperatures of the gas plating chambers and 30 are adjusted to supply a temperature sufficient to bring about thermal decomposition of the rare earth metal gaseous compound which is admitted into the gas plating chamber and in contact with the material to be gas plated.

The gas is passed into the chamber during plating, and which rare earth metal compound, admixed with helium or argon, will flow at a uniform rate into the chamber and be brought in contact with the object or workpiece to be plated. The workpiece is maintained at a temperature sufficient to cause the metal-bearing gas to decompose and deposit the rare earth metal on the surface. Waste gas products are carried out through the exhaust, and undecomposed compound may be recoveerd in the U-trap or other recovery means.

' The time of plating is controlled during carrying out of the process so that the desired coating of rare earth metal will be deposited. Generally, a plating of a few minutes will deposit .01 to .10 inch of the rare earth metal.

To illustrate the invention and method, the following examples of gas plating of certain of the rare earth metals is given. However, the invention is not limited to these particular metals but is exemplary of the entire group.

Example I Cerium metal is deposited on a metal disc substrate using cerium acetylace-tonate, the acetylacetonate being decomposed at a temperature of approximately 550 C. in an oxygen-free atmosphere. Gaseous cerium acetylacetonate is circulated through the gas plating chamber with argon carrier gas and in contact with the heated substrate, and under a subatmospheric pressure of 1 mm. Hg. The substrate is heated to a temperature to effect thermal decomposition of the rare earth metal acetylacetonate whereby pure cerium metal is deposited on the surface of the substrate.

The temperature employed to efiect the thermal decomposition of rare earth metal compounds will vary depending upon the compound employed as aforementioned, but in general the temperature lies below about 800 C.

In place of the rare earth acetylacetonates, the hydrides and nitrides of rare earths may be used. In this case the temperature of decomposition is somewhat higher and on the order of 600-1000 C. Rare earth metallic hydrides having the formula RI-I may be formed directly from the rare earth metals by hydrogenation using dry hydrogen and wherein the hydrogen is carefully purified.

Example 11 Gadolinium hydride is volatilized and introduced with helium as a carrier gas and subjected to a temperature of Example III Samarium iodide is volatilized at approximately 550 C. and introduced with the carrier gas of argon to the gas plating chamber, where it is decomposed to deposit the Samarium at a temperature of around 800'900 C.

Example I V Cerium metal is deposited by reduction of the cerium amalgam, decomposition taking place at approximately 300-500 C. under ordinary atmospheric pressure conditions.

Where other compounds are available of the rare earth metals, such as the carbonyls, these compounds may also be used in carrying out the gas plating of the rare earth metals by thermal decomposition of the metal carbonyl.

Gas plating of the rare earth metals may be carried out to deposit the metal on the surface of various substrates, such as metal, paper, glass, and the like, as illustrated in the drawings. Further, by adjusting the flow of the gases and the temperature in the gas plating chamber as well as the temperature to which the substrate is heated, gas platin g of the rare earth metals may be carried out at relatively high speeds and without oxidation of the substrate or the rare earth metal being deposited thereon. Flow rates of the plating gas may be readily maintained between 1 and 10 liters of inert carrier gas per minute with approximately by volume being carrier gas, and such as has been found effective. The particular flow rate and conditions may be readily chosen which are most eflicient for the specific materials being treated and the temperatures to be attained in the gas plating chamber. The time of exposure of the article or material to the plating metal bearing gas will determine the amount of metal deposit obtained.

It will be understood that this invention is susceptible to various modifications and substitutions of materials in order to carry out the invention and deposit the coating of the rare earth metals, and such modifications as fall within the appended claims are intended to be included herein.

What I claim is:

1. A method of gas plating cerium metal on a metal substrate surface and which consists in establishing said substrate surface to be gas plated with cerium in a chamber, circulating through said chamber a mixture of argon and vapors of cerium acetylacetonate, maintaining a subatmospheric pressure of 1 mm. Hg, and concurrently heating the metal substrate to be plated to a temperature of approximately 550 C. to cause thermal decomposition of the cerium acetylacetonate and deposition of cerium metal on the heated substrate metal surface.

2. A product produced in accordance with the method set forth in claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,400,255 Pfeil May 14, 1946 2,785,651 Pawlyk Mar. 19, 1957 FOREIGN PATENTS 64,678 Germany Sept. 27, 1892 487,854 Great Britain Sept. 22, 1936 

1. A METHOD OF GAS PLATING CERIUM METAL ON A METAL SUBSTRATE SURFACE AND WHICH CONSISTS IN ESTABLISHING SAID SUBSTRATE SURFACE TO BE GAS PLATED WITH CERIUM IN A CHAMBER, CIRCULATING THROUGH SAID CHAMBER A MIXTURE OF ARGON AND VAPORS OF CERIUM ACETYLACETONATE, MAINTAING A SUBATMOSPHERIC PRESSURE OF 1MM. HG,AND CONCURRENTLY HEATING THE METAL SUBSTRATE TO BE PLATED TO A TEMPERATURE OF APPROXIMATELY 550*C. TO CAUSE THERMAL DECOMPOSITION OF THE CERIUM ACETYLACETONATE AND DEPOSITION OF CERIUM METAL ON THE HEATED SUBSTRATE METAL SURFACE. 